The present invention relates to the incorporation of dopant impurities, particularly to depositing dopant impurities in the surface of a semiconductor, and more particularly to an enhanced doping process involving deposition of a dopant on the semiconductor surface followed by melting of the surface and drive-in of the dopant using pulsed energy to be absorbed near the surface.
Various techniques have been developed for incorporating a dopant into a material. One of these techniques is known as Gas Immersion Laser Doping (GILD). The GILD technique involves irradiating a material, such as a semiconductor surface, with a pulsed laser in the presence of a dopant ambient (such as BF.sub.3, PF.sub.5, AsH.sub.3, etc.). The GILD process relies on the dopant molecules adsorbing on the semiconductor surface, the laser pulse melting a surface region of the semiconductor, the dopant being incorporated into the molten region of the semiconductor, and the molten region solidifying after the laser pulse, the dopant atoms being electrically active after solidification of the semiconductor. Using the GILD technique, the maximum dose of electrically active dopant atoms per pulse is limited to a fraction of the adsorbed dopant molecules (about 10.sup.13 cm.sup.-2). Useful dopant doses are above 5.times.10.sup.14 cm.sup.-2. Thus, the GILD technique requires at least 50 doping pulses for practical use.
The present invention involves a semiconductor doping process which enhances the dopant incorporation achieved using the GILD technique. The doping process of the present invention enhances the doping per pulse by increasing the surface concentration (and possibly thickness) of dopant molecules on the semiconductor surface prior to an energy pulse, thus resulting in a greater dose of dopant per pulse. Thus, by the two-step process of the invention involving: 1) dopant deposition onto a semiconductor surface, and 2) dopant incorporation in the semiconductor by pulsed laser or pulsed ion beam energy, the number of pulses required to achieve useful active dopant concentrations is significantly reduced compared to the GILD technique. The deposition of the dopant on the semiconductor surface can be accomplished by a number of known deposition techniques. The energy pulse may be either that of a pulsed laser or of a pulsed ion-beam source.